1. Field of the Invention
The invention relates to instruments for measuring the clearance between the body side bearings of rail cars and the subjacent truck side bearing rollers.
2. Description of the Prior Art
The Association of American Railroad's Interchange Rule 47, E.2.a. states in part that: "Side bearings must have 3/16 minimum to 5/16 inch maximum clearance."
As is well known in the railroad industry, the side bearings of the clearance type referred to in the Rule are elongated, fore and aft oriented, wedge-shaped-in-cross-section slabs of metal mounted on the bottom of the rail car body. There is one side bearing on each side of each of the car body center plates, each side bearing being located transversely from the center plate a predetermined distance such that when the body is lowered onto its trucks and the body center plates engage and are supported on the respective center plate bowls of the truck bolsters, the central zones of the body side bearings are ideally spaced 3/16 to 5/16 inch above the top of the respective subjacent truck side bearing rollers located in roller cages on the truck bolsters.
As the car body tilts from side to side for various reasons, such as going around a curve in the track, the body side bearings on the lower side of the tilt engage and are temporarily supported by the subjacent truck side bearing rollers.
If the maximum specified clearance of 5/16" is exceeded, the needed support is not provided at the appropriate juncture and the car can tilt to an unwanted degree. If, on the other hand, there is less than the minimum specified clearance, an excessive load is imposed upon the underlying roller and the center plate is tilted upwardly out of full engagement with the center plate bowl, thereby creating a high derailment risk.
Clearance measurements and adjustments are made periodically to minimize these undesirable consequences. Once the clearance of the body side bearings is determined and is found to be outside the specified range of 3/16" to 5/16", correction is made by adding or removing shims, or by changing the existing roller to another roller having a diameter such as to achieve the specified clearance.
Heretofore, various types of gauges have been employed to determine the extent of the clearance.
An early type was a device called a step gauge in which an elongated bar was cut with stepped increments. The step gauge is now rarely, if ever, used.
A widely-used, more recent type of measuring device has been the Pratt-Whitney No. 713 lateral gauge. The lateral gauge, for greatest accuracy, requires that the rail track be level, that the rail car body be perfectly balanced on its truck bolsters and that there be no twist in the car super-structure. Unfortunately, these ideal conditions rarely exist. Thus, even the most careful and conscientious craftsman, using the lateral gauge, will often find that when the rail car with corrected clearance is moved to another location the clearance is again found to be outside the specified range and the entire procedure of shimming etc. must be repeated.
The present gauge operates on a different principle from that of the lateral gauge and marks an improvement of a whole order over previous clearance gauges.
A preliminary search was made for gauges of the present type and the following U.S. patents were revealed:
______________________________________ Bourgeois 1,509,703 9/23/1924 Brienza 1,863,236 6/14/1932 Komstadius 3,158,941 12/01/1964 Colby 4,321,754 3/30/1982 ______________________________________
Copies of these four patents are enclosed, herewith.
Of these four patents, only Brienza and Komstadius show a structural similarity to the present device; but neither of these patents discloses an instrument which first measures "down" against three linear surfaces and then measures "up" against three linear surfaces to establish the extent of clearance between the registering surfaces located at the opposite extremities of the instrument, as does the present gauge.